used. The alloy LA 141 had been used by IBM on the Gemini keyboard, read out units, and computer in small quantities and the larger frame of the LVDC was produced from the largest billets of LA 141 cast at the time and subsequently CNC machined into the frame. A page consisted of two boards back to back and a magnesium-lithium frame to conduct heat to the chassis. The 12-layer boards contained signal, power, and ground layers and connections between layers were made by plated-through holes. Up to 35 alumina squares of could be reflow soldered to a board. These alumina squares had conductors silk screened to the top side and resistors silk-screened to the bottom side. Semiconductor chips of , each containing either one transistor or two diodes, were reflow soldered to the top side. The complete module was called a unit logic device. The unit logic device (ULD) was a smaller version of IBM's Solid Logic Technology (SLT) module, but with clip connections. Copper balls were used for contacts between the chips and the conductive patterns. The hierarchy of the electronic structure is shown in the following table. Gallery See also Apollo Guidance Computer Apollo PGNCS primary spacecraft guidance system Gemini Spacecraft On-Board Computer (OBC) Notes References IBM, Saturn V Launch Vehicle Digital Computer, Volume One: General Description and Theory, 30 November 1964 IBM, Saturn V Guidance Computer, Semiannual Progress Report, 1 Apr. - 30 Sep. 1963, 31 October 1963; archive Bellcomm, Inc, Memory Requirements for the Launch Vehicle Digital Computer (LVDC), April 25, 1967 Boeing, Saturn V Launch Vehicle Guidance Equations, SA-504, 15 July 1967 NASA Marshall Spaceflight Center, Saturn V Flight Manual SA-503, 1 November 1968 NASA Marshall Spaceflight Center, Skylab Saturn IB Flight Manual, 30 September 1972 M.M. Dickinson, J.B. Jackson, G.C. Randa. IBM Space Guidance Center, Owego, NY. "Saturn V Launch Vehicle Digital Computer and Data Adapter." Proceedings of the Fall Joint Computer Conference, 1964, pages 501–516. S. Bonis, R. Jackson, and B. Pagnani. IBM Space Guidance Center, Owego, NY. "Mechanical and Electronic Packaging for a Launch-Vehicle Guidance Computer." International Electronic Circuit Packaging Symposium 21–24 August 1964. Pages 226–241. IBM, Apollo Study Report, Volume 2. IBM Space Guidance Center, Owego, NY, 1 October 1963. 133 pages. Also available on Virtual AGC (search for 63-928-130). NASA MSFC, Astrionics System Handbook Saturn Launch Vehicles NASA Marshall Space Flight Center, 1 Nov 1968. MSFC No. IV-4-401-1. IBM